Abstract: Opioid and psychostimulant addictions are large and growing public health concerns that are inadequately managed with available therapeutics. The objective of this proposal directly addresses this unmet clinical need, as it includes the evaluation of a novel anti-addiction therapeutic strategy. A shared feature of addictive drugs is their ability to induce inappropriate activation of the mesolimbic dopamine system. Restoration of dopamine signaling homeostasis may be achieved by targeting the G protein-coupled receptor (GPCR) neurotensin receptor 1 (NTR1). NTR1 modulates dopamine signaling via action at putative NTR1/dopamine receptor D2 (D2R) complexes. The efficacy of peptide or small molecule NTR1 agonists in animal models of addiction have made them highly desirable but they all have side effects. NTR1, like other GPCRs, signals through both G protein- and ?-arrestin-mediated pathways. Recently, we have developed and characterized a novel class of small molecule NTR1 ligands, typified by compound SBI-553, which activates ?-arrestin without stimulating G protein signaling. This type of functional selectivity/biased siganling presents an opportunity to produce more directed physiological action and reduce unwanted side effects. My promising initial findings suggest that SBI-553 attenuates opioid and stimulant-associated behaviors in mice without the hypotension and hypothermia characteristic of unbiased NTR1 agonism. The objectives of this application are to elucidate the mechanism by which ?-arrestin biased NTR1 ligands attenuate drug-associated behaviors and validate their therapeutic potential by integrating murine self-administration and functional neuroimaging. My central hypothesis is that selective ?-arrestin activation at NTR1 attenuates addiction-like behaviors and associated changes in regional brain metabolism through antagonism of D2R function. This hypothesis will be tested by pursuing three specific aims, using SBI-553 as a tool compound. I will first (1) K99) define the behavioral effects of ?-arrestin biased NTR1 ligands by conducting self-administration studies in genetically engineered mice. I will then (2) K99) determine the physiological effects of ?-arrestin biased NTR1 ligands using state-of-the-art small animal positron emission tomography/computed tomography (PET/CT). Finally, I will use my new training in murine self-administration and PET/CT to independently (3) R00) evaluate the contribution of D2R to the effects of ?-arrestin biased NTR1 ligands. Pursuit of these aims requires interdisciplinary training in animal models of addiction and neuroimaging to complement my previous studies in molecular biology. Therefore, I have assembled expert collaborators into an interdisciplinary mentoring committee, chaired by Drs. Marc Caron (Mentor) and Lawrence Barak (Co-Mentor). The Caron laboratory at Duke University is uniquely well-positioned to answer questions regarding biased GPCR signaling. We have developed an individualized training plan that will provide me with the scientific and professional skills required to run a productive, independent laboratory and study addiction as a brain disease, including its neurological etiology and behavioral manifestations.